Discharge tubes such as CCFL or cold cathode fluorescent lamps filled with discharge gas including argon and mercury, have been widely used as a backlight source for displays such as liquid crystal display (LCD). Discharge tube comprises a glass tube filled with mercury and noble gas such as neon, argon or xenon, a pair of electrodes positioned at opposite inner ends of glass tube, and a fluorescent film coated on inner surface of glass tube. Each of electrodes in discharge tube is connected to one end of a lead terminal, the other end of which extends through each end of glass tube to outside. When voltage is applied between a pair of electrodes, electrons are emitted from one of electrodes to produce ultraviolet rays when electrons impinge mercury atoms in glass tube. Ultraviolet rays are converted in wavelength into a visible ray through fluorescent film on inner surface of glass tube, and discharged to outside of glass tube for illumination.
FIG. 18 illustrates a remote controller 8 and a display device such as liquid crystal display television (LCDTV) which has a built-in discharge tube as a backlight source. Display device comprises a display 1 and a lighting device 30 which has a built-in discharge tube not shown as a backlight source. Typically, display device comprises an infrared receiver 6 which can receive infrared signals 21 from remote controller 8 for remote control of for example grazing or switching channels of television. Infrared receiver 6 comprises a light receiving element such as photo-transistor for sensing infrared signals 21 of approximately 910 nm (nanometers) transmitted from remote controller 8.
FIG. 19 is a graph showing a level or mean power level of electric power supplied to discharge tube of prior art display device with time passage. As shown in FIG. 19, after a switch for display device is turned on until turned off, prior art display device continuously supplies a constant AC power set in display device to a discharge tube throughout the first, second and third periods regardless of non-indicative and display periods which respectively deactivates and activates screen of display period. Specifically, the first period denotes a non-indicative time interval of display 1 that starts with completing setting-up of display 1 and terminates with or before indication of screen. The second period denotes a time interval that starts with termination of the first period and extends to an initial stage of indicative time interval of screen after completing setting-up of display 1. The third period denotes a time interval that starts with termination of the second period and terminates when electric input (voltage, current or power) to discharge tube comes to a rated value.
Display device of this type is defective in that it cannot be appropriately controlled by remote controller 8 at the initial stage of indicative time interval for displaying screen because discharge tube disadvantageously irradiates infrared ray which has an undesirable impact on receiving operation by infrared receiver 6. Discharge tube irradiates a light 22 inclusive of visible light and infrared ray of 910 nm in wavelength emitted from discharge gas (argon gas) filled in discharge tube. When a tube voltage is applied between a pair of electrodes of discharge tube to turn discharge tube on, discharge tube sends out light through display screen to outside, and a part of emitted light reaches infrared receiver 6 after reflection on floor, walls or other objects. As a result, infrared receiver 6 cannot distinguish infrared signals 21 of remote controller 8 from infrared ray contained in light 22 out of discharge tube so that infrared ray from discharge tube inconveniently prevents prompt and correct control such as switching channels in display device through infrared signals 21 of remote controller 8 at the initial stage during the indicative time interval for indicating screen of display 1. To avoid such obstruction by infrared ray from discharge tube, for example, Japanese Patent Disclosure No. 2002-323860 has suggested provision of an additional member such as a shutoff sheet disposed adjacent to backlight for interrupting infrared ray therefrom.
However, provision of the additional member such as shutoff sheet would disadvantageously raise cost in manufacture of display device. In another aspect, it seems very difficult to selectively cut off only infrared ray without attenuation of visible light, and also in this view, it is unpractical to provide the additional member such as shutoff sheet.
Accordingly, an object of the present invention is to provide an electricity controller, a device for lighting discharge tube, a display device and an electric power control method that can restrain infrared ray in a light emitted from a discharge tube by controlling operation of drive circuits in the device for lighting discharge tube without need of any additional member such as shutoff sheet against infrared ray.
Another object of the present invention is to provide an electricity controller, a device for lighting discharge tube, a display device and an electric power control method that can overcome the malfunction uncontrollable by a remote controller at the initial stage immediately after the screen indication of display.